The present invention relates to jacketing steel pipes and more particularly the invention relates to a roller for pressing thermoplastic strips onto the surfaces of steel pipes for purposes of jacketing them by helically wrapping such strips around the pipe.
Steel pipes are jacketed for example in that a freshly extruded polyethylene strip is wound helically upon an axially movable and rotating pipe. An adhesive is also applied to the pipe in that a ribbon made of highly viscous, adhesive material is also freshly extruded and wrapped around the pipe to be located between the pipe's surface and the polyethylene strip. See e.g. U.S. Pat. Nos. 3,616,006 and 3,823,045.
Generally speaking, these known methods wind strip material in overlaying loops and the strip is forced against the pipe's surface by means of solid, plastic rolls or rollers for purposes of welding the edges of the strip and for smoothing the surface contour of the overlap.
German printed patent application No. 1,901,245 discloses a basically similar method but for jacketing corrugated tubes. The strip is forced against the tube's surface by means of an air filled rather soft hose being supported by pulleys in surface portions facing away from the tube. This hose is made from a heat resisting material such as silicon rubber and runs like a pulley while being driven by the rotating tube. The hose conforms to the contour of the corrugated tube and forces the strip material onto the ridges as well as into the valleys of the corrugation. However, the invention does not relate to such a device.
It has been found, that the known pressure rolls do not perform adequately. For example, it was found that they do not completely avoid the inclusion of air bubbles between the pipe's surface and the strip material.